High temperature superconductor synchronous rotor coil support insulator

ABSTRACT

A rotor having a superconducting coil winding is disclosed having a rotor core having at least one conduit extending through the core; at least one tension rod extending between the pair of side sections of the coil winding and through said at least one conduit of the rotor; and an insulator in the conduit thermally separating the tension rod from the rotor.

RELATED APPLICATIONS

[0001] This application is related to U.S. Pat. No. ______ (U.S. patentapplication Ser. No. 09/855,026), filed May 15, 2001, and incorporatedby reference in its entirety herein.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to a superconducting coilin a synchronous rotating machine. More particularly, the presentinvention relates to a support structure for superconducting fieldwindings in the rotor of a synchronous machine.

[0003] Synchronous electrical machines having field coil windingsinclude, but are not limited to, rotary generators, rotary motors, andlinear motors. These machines generally comprise a stator and rotor thatare electromagnetically coupled. The rotor may include a multi-polerotor core and one or more coil windings mounted on the rotor core. Therotor cores may include a magnetically-permeable solid material, such asan iron-core rotor.

[0004] Conventional copper windings are commonly used in the rotors ofsynchronous electrical machines. However; the electrical resistance ofcopper windings (although low by conventional measures) is sufficient tocontribute to substantial heating of the rotor and to diminish the powerefficiency of the machine. Recently, superconducting (SC) coil windingshave been developed for rotors. SC windings have effectively noresistance and are highly advantageous rotor coil windings.

[0005] Iron-core rotors saturate at an air-gap magnetic field strengthof about 2 Tesla. Known superconducting rotors employ air-core designs,with no iron in the rotor, to achieve air-gap magnetic fields of 3 Teslaor higher. These high air-gap magnetic fields yield increased powerdensities of the electrical machine, and result in significant reductionin weight and size of the machine. Air-core superconducting rotorsrequire large amounts of superconducting wire. The large amounts of SCwire add to the number of coils required, the complexity of the coilsupports, and the cost of the SC coil windings and rotor.

[0006] High temperature SC coil field windings are formed ofsuperconducting materials that are brittle, and must be cooled to atemperature at or below a critical temperature, e.g., 27° K, to achieveand maintain superconductivity. The SC windings may be formed of a hightemperature superconducting material, such as a BSCCO(Bi_(x)Sr_(x)Ca_(x)Cu_(x)O_(x)) based conductor.

[0007] Superconducting coils have been cooled by liquid helium. Afterpassing through the windings of the rotor, the hot, used helium isreturned as room-temperature gaseous helium. Using liquid helium forcryogenic cooling requires continuous reliquefaction of the returned,room-temperature gaseous helium, and such reliquefaction posessignificant reliability problems and requires significant auxiliarypower.

[0008] Prior SC coil cooling techniques include cooling anepoxy-impregnated SC coil through a solid conduction path from acryocooler. Alternatively, cooling tubes in the rotor may convey aliquid and/or gaseous cryogen to a porous SC coil winding that isimmersed in the flow of the liquid and/or gaseous cryogen. However,immersion cooling requires the entire field winding and rotor structureto be at cryogenic temperature. As a result, no iron can be used in therotor magnetic circuit because of the brittle nature of iron atcryogenic temperatures.

[0009] What is needed is a superconducting field winding assemblage foran electrical machine that does not have the disadvantages of theair-core and liquid-cooled superconducting field winding assemblages of,for example, known superconducting rotors.

[0010] In addition, high temperature superconducting (HTS) coils aresensitive to degradation from high bending and tensile strains. Thesecoils must undergo substantial centrifugal forces that stress and strainthe coil windings. Normal operation of electrical machines involvesthousands of start-up and shut-down cycles over the course of severalyears that result in low cycle fatigue loading of the rotor.Furthermore, the HTS rotor winding should be capable of withstanding 25%over-speed operation during rotor balancing procedures at ambienttemperature, and notwithstanding occasional over-speed conditions atcryogenic temperatures during power generation operation. Theseover-speed conditions substantially increase the centrifugal forceloading on the windings over normal operating conditions.

[0011] SC coils used as the HTS rotor field winding of an electricalmachine are subjected to stresses and strains during cool-down andnormal operation. They are subjected to centrifugal loading, torquetransmission, and transient fault conditions. To withstand the forces,stresses, strains and cyclical loading, the SC coils should be properlysupported in the rotor by a coil support system. These support systemshold the SC coil(s) in the HTS rotor and secure the coils against thetremendous centrifugal forces due to the rotation of the rotor.Moreover, the coil support system protects the SC coils, and ensuresthat the coils do not prematurely crack, fatigue or otherwise break.

[0012] Developing support systems for HTS coil has been a difficultchallenge in adapting SC coils to HTS rotors. Examples of coil supportsystems for HTS rotors that have previously been proposed are disclosedin U.S. Pat. Nos. 5,548,168; 5,532,663; 5,672,921; 5,777,420; 6,169,353,and 6,066,906. However, these coil support systems suffer variousproblems, such as being expensive, complex and requiring an excessivenumber of components. There is a long-felt need for a HTS rotor having acoil support system for a SC coil. The need also exists for a coilsupport system made with low cost and easy-to-fabricate components.

BRIEF SUMMARY OF THE INVENTION

[0013] A coil support structure having tension rods and U-shaped channelhousings is disclosed for mounting SC coils inside the vacuum space of aHTS rotor. The tension rods span opposite sides of a coil. Channelhousings are attached to both ends of the tension rod and wrap around aside portion of the coil. The coil is supported by the tension rods andchannel housings with respect to centrifugal and other forces that acton the coil.

[0014] The HTS rotor may be for a synchronous machine originallydesigned to include SC coils. Alternatively, the HTS rotor may replace acopper coil rotor in an existing electrical machine, such as in aconventional generator. The rotor and its SC coils are described here inthe context of a generator, but the HTS coil rotor is also suitable foruse in other synchronous machines.

[0015] The coil support system is useful in integrating the coil supportsystem with the coil and rotor. In addition, the coil support systemfacilitates easy pre-assembly of the coil support system, coil and rotorcore prior to final rotor assembly. Pre-assembly reduces coil and rotorassembly time, improves coil support quality, and reduces coil assemblyvariations.

[0016] One embodiment of the invention is a synchronous machine, a rotorcomprising: a rotor core having at least one conduit extending throughthe core; a super-conducting coil winding extending around at least aportion of the rotor core, said coil winding having a pair of sidesections on opposite sides of said rotor core; at least one tension rodextending between the pair of side sections of the coil winding andthrough said at least one conduit of the rotor; and an insulator in theconduit thermally separating the tension rod from the rotor.

[0017] A further embodiment of the invention is a method for supportinga super-conducting coil winding on a rotor core of a synchronous machinecomprising the steps of:

[0018] a. extending a tension rod through a conduit in said rotor core;

[0019] b.supporting the tension rod in the conduit by a first insulatortube;

[0020] c. inserting a housing over a portion of the coil;

[0021] d. attaching an end of the tension rod to the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings in conjunction with the text of thisspecification describe an embodiment of the invention.

[0023]FIG. 1 is a schematic side elevational view of a synchronouselectrical machine having a superconducting rotor and a stator.

[0024]FIG. 2 is a perspective view of an exemplary racetracksuperconducting coil winding.

[0025]FIG. 3 is an exploded view of the components of a high temperaturesuperconducting (HTS) rotor.

[0026] FIGS. 4 to 6 are schematic cross-sectional views of the HTS rotorshown in FIG. 3.

[0027]FIG. 7 is an enlarged cross-sectional view of a portion of a coilsupport structure for the HTS rotor shown in FIG. 3.

[0028]FIG. 8 is a perspective view of a channel housing.

[0029] FIGS. 9 to 11 are perspective views showing the assembly processfor the HTS rotor shown in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

[0030]FIG. 1 shows an exemplary synchronous generator machine 10 havinga stator 12 and a rotor 14. The rotor includes field winding coils thatfit inside the cylindrical rotor vacuum cavity 16 of the stator. Therotor fits inside the rotor vacuum cavity of the stator. As the rotorturns within the stator, a magnetic field 18 (illustrated by dottedlines) generated by the rotor and rotor coils moves/rotates through thestator and creates an electrical current in the windings of the statorcoils 19. This current is output by the generator as electrical power.

[0031] The rotor 14 has a generally longitudinally-extending axis 20 anda generally solid rotor core 22. The solid core 22 has high magneticpermeability, and is usually made of a ferromagnetic material, such asiron. In a low power density superconducting machine, the iron core ofthe rotor is used to reduce the magnetomotive force (MMF), and, thus,minimize the amount of superconducting (SC) coil wire needed for thecoil winding. For example, the solid iron rotor core may be magneticallysaturated at an air-gap magnetic field strength of about 2 Tesla.

[0032] The rotor 14 supports at least one longitudinally-extending,racetrack-shaped, high-temperature superconducting (HTS) coil winding 34(See FIG. 2). The HTS coil winding may be alternatively a saddle-shapeor have some other shape that is suitable for a particular HTS rotordesign. A coil support system is disclosed here for a racetrack SC coilwinding. The coil support system may be adapted for coil configurationsother than a racetrack coil mounted on a solid rotor core.

[0033] The rotor includes a collector shaft 24 and a drive end shaft 30that bracket the rotor core 22, are supported by bearings 25. The endshafts may be coupled to external devices. For example, the endcollector shaft 24 has a cryogen transfer coupling 26 to a source ofcryogenic cooling fluid used to cool the SC coil windings in the rotor.The cryogen transfer coupling 26 includes a stationary segment coupledto a source of cryogen cooling fluid and a rotating segment whichprovides cooling fluid to the HTS coil. The collector end shaft 24 alsoincludes a collector 78 for electrically connecting to the rotating SCcoil winding. The drive end shaft 30 of the rotor may be driven by apower turbine coupling 32.

[0034]FIG. 2 shows an exemplary HTS racetrack field coil winding 34. TheSC field winding coils 34 of the rotor includes a high temperaturesuperconducting (SC) coil 36. Each SC coil includes a high temperaturesuperconductor, such as a BSCCO (Bi_(x)Sr_(x)Ca_(x)Cu_(x)O_(x))conductor wires laminated in a solid epoxy impregnated windingcomposite. For example, a series of BSCCO 2223 wires may be laminated,bonded together and wound into a solid epoxy impregnated coil.

[0035] SC wire is brittle and easy to be damaged. The SC coil istypically layer wound SC tape that is epoxy impregnated. The SC tape iswrapped in a precision coil form to attain close dimensional tolerances.The tape is wound around in a helix to form the racetrack SC coil 36.

[0036] The dimensions of the racetrack coil are dependent on thedimensions of the rotor core. Generally, each racetrack SC coilencircles the magnetic poles of the rotor core, and is parallel to therotor axis. The coil windings are continuous around the racetrack. TheSC coils form a resistance-free electrical current path around the rotorcore and between the magnetic poles of the core. The coil has electricalcontacts 114 that electrically connect the coil to the collector 78.

[0037] Fluid passages 38 for cryogenic cooling fluid are included in thecoil winding 34. These passages may extend around an outside edge of theSC coil 36. The passageways provide cryogenic cooling fluid to the coiland remove heat from the coil. The cooling fluid maintains the lowtemperatures, e.g., 27° K, in the SC coil winding needed to promotesuperconducting conditions, including the absence of electricalresistance in the coil. The cooling passages have an input and outputfluid ports 112 at one end of the rotor core. These fluid (gas) ports112 connect the cooling passages 38 on the SC coil to the cryogentransfer coupling 26.

[0038] Each HTS racetrack coil winding 34 has a pair ofgenerally-straight side portions 40 parallel to a rotor axis 20, and apair of end portions 54 that are perpendicular to the rotor axis. Theside portions of the coil are subjected to the greatest centrifugalstresses. Accordingly, the side portions are supported by a coil supportsystem that counteract the centrifugal forces that act on the coil.

[0039]FIG. 3 shows an exploded view of a rotor core 22 and coil supportsystem for a high temperature superconducting coil. The support systemincludes tension rods 42 connected to U-shaped channel housings. Thehousings hold and support the side portions 40 of the coil winding 38 inthe rotor. While one tension rod and channel housing is shown in FIG. 3,the coil support system will generally include a series of tension rodsthat each have coil support housings at both ends of the rod. Thetension rods and channel housings prevent damage to the coil windingduring rotor operation, support the coil winding with respect tocentrifugal and other forces, and provide a protective shield for thecoil winding.

[0040] The principal loading of the HTS coil winding 34 in an iron corerotor is from centrifugal acceleration during rotor rotation. Aneffective coil structural support is needed to counteract thecentrifugal forces. The coil support is needed especially along the sidesections 40 of the coil that experience the most centrifugalacceleration. To support the side sections of the coil, the tension rods42 span between the sections of the coil and attach to the channelhousings 44 that grasp opposite side sections of the coil. The tensionrods extend through conduits 46, e.g., apertures, in the rotor core sothat the rods may span between side sections of the same coil or betweenadjacent coils.

[0041] The conduits 46 are generally cylindrical passages in the rotorcore having a straight axis. The diameter of the conduits issubstantially constant, except at their ends near the recessed surfacesof the rotor. At their ends, the conduits may expand to a largerdiameter to accommodate a non-conducting cylindrical sleeve (insulatortube) 52 that provides slidable bearing surface and thermal isolationbetween the rotor core and the tension rod.

[0042] The axes of the conduits 46 are generally in a plane defined bythe racetrack coil. In addition, the axes of the conduits areperpendicular to the side sections of the coil to which are connectedthe tension rods that extends through the conduits. Moreover, theconduits are orthogonal to and intersect the rotor axis, in theembodiment shown here. The number of conduits and the location of theconduits will depend on the location of the HTS coils and the number ofcoil housings (see FIG. 10) needed to support the side sections of thecoils.

[0043] The tension rods support the coil especially well with respect tocentrifugal forces as the rods extend substantially radially between thesides of the coil winding. Each tension rod is a shaft with continuityalong the longitudinal direction of the rod and in the plane of theracetrack coil. The longitudinal continuity of the tension rods provideslateral stiffness to the coils which provides rotor dynamics benefits.Moreover, the lateral stiffness permits integrating the coil supportwith the coils so that the coil can be assembled with the coil supportprior to final rotor assembly. Pre-assembly of the coil and coil supportreduces production cycle, improves coil support quality, and reducescoil assembly variations. The racetrack coil is supported by an array oftension members that span the long sides of the coil. The tension rodcoil support members are pre-assembled to coil.

[0044] The HTS coil winding and structural support components are atcryogenic temperature. In contrast, the rotor core is at ambient “hot”temperature. The coil supports are potential sources of thermalconduction that would allow heat to reach the HTS coils from the rotorcore. The rotor becomes hot during operation. As the coils are to beheld in super-cooled conditions, heat conduction into the coils is to beavoided. The rods extend through apertures, e.g., conduits, in the rotorbut are not in contact with the rotor. This lack of contact avoids theconduction of heat from the rotor to the tension rods and coils.

[0045] To reduce the heat leaking away from the coil, the coil supportis minimized to reduce the thermal conduction through support from heatsources such as the rotor core. There are generally two categories ofsupport for superconducting winding: (i) “warm” supports and (ii) “cold”supports. In a warm support, the supporting structures are thermallyisolated from the cooled SC windings. With warm supports, most of themechanical load of a superconducting (SC) coil is supported bystructural members spanning from cold to warm members.

[0046] In a cold support system, the support system is at or near thecold cryogenic temperature of the SC coils. In cold supports, most ofthe mechanical load of a SC coil is supported by structural memberswhich are at or near a cryogenic temperature. The exemplary coil supportsystem disclosed here is a cold support in that the tension rods andassociated housings that couple the tension rods to the SC coil windingsare maintained at or near a cryogenic temperature. Because thesupporting members are cold, these members are thermally isolated, e.g.,by the non-contact conduits through the rotor core, from other “hot”components of the rotor.

[0047] An individual support member consists of a tension rod 42 (whichmay be a bar and a pair of bolts at either end of the bar), a channelhousing 44, and a dowel pin 80 that connects the housing to the end ofthe tension rod. Each channel housing 44 is a U-shaped bracket havinglegs that connect to a tension rod and a channel to receive the coilwinding 34. The U-shaped channel housing allows for the precise andconvenient assembly of the support system for the coil. A series ofchannel housings may be positioned end-to-end along the side of the coilwinding. The channel housings collectively distribute the forces thatact on the coil, e.g., centrifugal forces, over substantially the entireside sections 40 of each coil.

[0048] The channel housings 44 prevent the side sections 40 of the coilsfrom excessive flexing and bending due to centrifugal forces. The coilsupports do not restrict the coils from longitudinal thermal expansionand contraction that occur during normal start/stop operation of the gasturbine. In particular, thermal expansion is primarily directed alongthe length of the side sections. Thus, the side sections of the coilslide slightly longitudinally with respect to the channel housing andtension rods.

[0049] The transfer of the centrifugal load from the coil structure to asupport rod is through the channel housing that fits around the coiloutside surface and side straight sections, and is doweled by pins 80 toa wide diameter end of the tension rod. The U-shaped channel housingsare formed of a light, high strength material that is ductile atcryogenic temperatures. Typical materials for channel housing arealuminum, Inconel, or titanium alloys, which are non-magnetic. The shapeof the U-shaped housing may be optimized for low weight and strength.

[0050] The dowel pin 80 extends through apertures in the channel housingand tension rod. The dowel may be hollow for low weight. Locking nuts(not shown) are threaded or attached at the ends of the dowel pin tosecure the U-shaped housing and prevent the sides of the housing fromspreading apart under load. The dowel pin can be made of high strengthInconel or titanium alloys. The tension rods are made with largerdiameter ends 82 that are machined with two flats 86 at their ends tofit the U-shaped housing and coil width. The flat ends 86 of the tensionrods abut the inside surface of the HTS coils, when the rod, coil andhousing are assembled together. This assembly reduces the stressconcentration at the hole in the tension rod that receives the dowel.

[0051] The coil support system of tension rods 42, channel housings 44and split-clamp 58 may be assembled with the HTS coil windings 34 asboth are mounted on the rotor core 22. The tension rods, channelhousings and clamp provide a fairly rigid structure for supporting thecoil windings and holding the coil windings in place with respect to therotor core.

[0052] Each tension rod 42 extends through the rotor core, and mayextend orthogonally through the axis 20 of the rotor. Conduits 46through the rotor core provide a passage through which extend thetension rods. The diameter of the conduits is sufficiently large toavoid having the hot rotor walls of the conduits be in contact with thecold tension rods. The avoidance of contact improves the thermalisolation between the tension rods and the rotor core.

[0053] The rotor core 22 is typically made of magnetic material such asiron, while the rotor end shafts are typically made of non-magneticmaterial such as stainless steel. The rotor core and end shafts aretypically discrete components that are assembled and securely joinedtogether by either bolting or welding.

[0054] The iron rotor core 22 has a generally cylindrical shape suitablefor rotation within the rotor cavity 16 of the stator 12. To receive thecoil winding, the rotor core has recessed surfaces 48, such as flat ortriangular regions or slots. These surfaces 48 are formed in the curvedsurface 50 of the cylindrical core and extending longitudinally acrossthe rotor core. The coil winding 34 is mounted on the rotor adjacent therecessed areas 48. The coils generally extend longitudinally along anouter surface of the recessed area and around the ends of the rotorcore. The recessed surfaces 48 of the rotor core receive the coilwinding. The shape of the recessed area conforms to the coil winding.For example, if the coil winding has a saddle-shape or some other shape,the recess(es) in the rotor core would be configured to receive theshape of the winding.

[0055] The recessed surfaces 48 receive the coil winding such that theouter surface of the coil winding extend to substantially an envelopedefined by the rotation of the rotor. The outer curved surfaces 50 ofthe rotor core when rotated define a cylindrical envelope. This rotationenvelope of the rotor has substantially the same diameter as the rotorcavity 16 (see FIG. 1) in the stator.

[0056] The gap between the rotor envelope and stator cavity 16 is arelatively-small clearance, as required for forced flow ventilationcooling of the stator only, since the rotor requires no ventilationcooling. It is desirable to minimize the clearance between the rotor andstator so as to increase the electromagnetic coupling between the rotorcoil windings and the stator windings. Moreover, the rotor coil windingis preferably positioned such that it extends to the envelope formed bythe rotor and, thus, is separated from the stator by only the clearancegap between the rotor and stator.

[0057] The end sections 54 of the coil winding 34 are adjacent oppositeends 56 of the rotor core. A split-clamp 58 holds each of the endsections of the coil windings in the rotor. The split clamp at each coilend 54 includes a pair of opposite plates 60 between which is sandwichedthe coil winding 34. The surface of the clamp plates includes channels116, 118 (FIG. 11) to receive the coil winding and connections 112, 114to the winding.

[0058] The split clamp 58 may be formed of a non-magnetic material, suchas aluminum or Inconel alloys. The same or similar non-magneticmaterials may be used to form the tension rods, channel housings andother portions of the coil support system. The coil support system ispreferably non-magnetic so as to preserve ductility at cryogenictemperatures, since ferromagnetic materials become brittle attemperatures below the Curie transition temperature and cannot be usedas load carrying structures.

[0059] The split clamp 58 is surrounded by, but is not in contact withcollar 62. There is a collar 62 at each end of the rotor core 22,although only one collar is shown in FIG. 3. The collar is a thick diskof non-magnetic material, such as stainless steel, the same as orsimilar to the material, that forms the rotor shafts. Indeed, the collaris part of the rotor shaft. The collar has a slot 64 orthogonal to therotor axis and sufficiently wide to receive and clear the split clamp58. The hot sidewalls 66 of the slot collar are spaced apart from thecold split clamp so they do not come in contact with each other.

[0060] The collar 62 may include a recessed disk area 68 (which isbisected by the slot 64) to receive a raised disk region 70 of the rotorcore (see opposite side of rotor core for raised disk region to beinserted in opposite collar). The insertion of the raised disk region onthe end 56 of the rotor core into the recessed disk 68 provides supportto the rotor core in the collar, and assists in aligning the rotor coreand collars. In addition, the collar may have a circular array of boltholes 72 extending longitudinally through the collar and around the rimof the collar. These bolt holes correspond to matching threaded boltholes 74 that extend partially through the rotor core. Threaded bolts 75(see FIG. 5) extend through these longitudinal bolt holes 72, 74 andsecure the collars to the rotor core.

[0061]FIG. 4 is a first cross-sectional view of the rotor core andcollar. FIG. 5 is a second cross-sectional view of the rotor and collarthat is orthogonal to the first view. The electrical and cooling fluidconduits are shielded by a thin walled tube 76 that extends along therotor axis from one of the coil end sections 54 and through a collar 62.The cooling conduits in the tube 76 connect to the input and outputports 112 of the cooling passage 38 on the coil winding to the cryogenictransfer coupling 26. An electrical coupling 114 to the coil is providedat same end section of the coil as the cooling coupling 26.

[0062] The side sections 40 of the racetrack-shaped coil winding 34 aresupported by the series of tension rods 42 that extend through theconduits 46 in the rotor core. The tension rods are nonmagnetic,straight bars that extend between opposite side sections of the samecoil, or between side sections of the two coils. The tension rod may beformed of a high strength non-magnetic alloys, such as Inconel X718. Thetension rods have at each end a coupling with a channel housing 44 thatwraps around and holds the side 40 of the coil winding. The channelhousings 44 and the tension rods 42 may provide an adjustment of thetension applied to the side sections of the coil windings. For example,the tension rods may be formed of a tension bar that extends through therotor core and has at each end a threaded opening to receive a tensionbolt. The tension bolts may each have a flat face 86 that abuts the coilwinding.

[0063] The coil winding 34 is supported by the tension rods 42 (only oneof which is shown in FIG. 4) that span opposite side sections 40 of thecoil. The channel housing 44 is connected by a dowel pin 80 to the endof the tension rod. For illustrative purposes, the left side of FIG. 6shows the tension rod without a channel housing. Similarly, the upperside of FIG. 4 shows the tension rod 46 without a channel housing;whereas, the lower side shows a channel housing attached to the tensionrod. Tension rods 42 extend through the conduits 46 in the rotor core22. These conduits have increased diameters at their respective ends 88.These expanded ends 88 receive the insulator tube 52 which is formed asa sleeve on the tension rod. The insulator tubes thermally shield thetension rods 42 from the hot rotor core 22.

[0064] As shown in FIG. 5, the conduits 46 extend perpendicularlythrough the rotor axis and are symmetrically arranged along the lengthof the core. The number of conduits 46 and their arrangement on therotor core and with respect to each other is a matter of design choice.

[0065] The rotor core may be encased in a metallic cylindrical shield 90that protects the superconducting coil winding 34 from eddy currents andother electrical currents that surround the rotor and provides thevacuum envelope as required to maintain a hard vacuum around thecryogenic components of the rotor. The cylindrical shield 90 may beformed of a highly-conductive material, such as a copper alloy oraluminum.

[0066] The SC coil winding 34 is maintained in a vacuum. The vacuum maybe formed by the shield 90 which may include a stainless steelcylindrical layer that forms a vacuum vessel around the coil and rotorcore. The FIG. 7 is a cross-sectional diagram taken perpendicular to therotor axis and showing an enlarged portion of the rotor core 22, tensionrod 42, coil winding 34 and associated structures. The flat end 86 ofthe tension rod abuts an inside surface of the coil winding 34. Theopposite end of the tension rod (not shown in FIG. 7) abuts a similarinside surface of the opposite side of the coil winding. Thus, thetension rod spans between the coil winding and provides a fixed surface86 which supports the coil winding.

[0067] Each tension rod 42, although typically cylindrical along itslength, has flat ends 86, which permit close attachment to the coilwinding and U-shaped channel housing 44. Each tension rod is connectedto a channel housing 44 by a dowel pin 80, which prevents the housingfrom sliding radially outward from the tension rod. The channel housingprevents centrifugal force from bending or warping the coil while therotor is rotating. Locking nuts (not shown) are threaded at the ends ofthe dowel pin 80 to secure the housing 44 side legs 106 from spreadingapart under load. The dowel pin can be made from high strength Inconelor titanium alloys. Each tension rod 42 fits inside a non-contactconduit 46, such that the tension rod does not intentionally contact therotor core.

[0068] An iron-core rotor is designed to transmit the steady state andtransient torques primarily through the rotor body in contrast to theair-core rotor that transmits these torques directly to the rotorwinding. However, low level torques are still transmitted to the HTScoil and must be supported by thermally efficient robust thermalinsulators 52. The fiber reinforced composite insulator tubes 52 are thethermal insulators that support tangential forces acting on the HTScoil. The insulator tubes are preloaded in compression by retainer nuts84 threaded on the tension rods. The composite material of the insulatortubes is preferably glass fiber reinforced epoxy resin.

[0069] At the end of each tension rod, there may be an insulating tube52 that fastens the coil support structure to the hot rotor and reducesconduction heat transfer therebetween. Additionally, there may alock-nut 84 threaded on tension rod 42 that connects to the insulatingtube 52, and is used to secure and adjust the position of rod 42 insidethe conduit 46. The lock-nut 84 and the tube 52 secure the tension rodand channel housing to the rotor core while minimizing the heat transferfrom the hot rotor to the housing structure.

[0070] The insulator tube is formed of a thermal insulative material,such as a fiber reinforced composite material. One end of the tube mayinclude an external ring 120 that abuts the wall of the conduit 88. Theother end of the tube includes an internal ring 122 that engages thelock-nut 84 secured to an end of the tension rod. An insulator tube andlock-nut are at each end of the tension rod. Heat from the rotor wouldhave to conduct through the length of the insulator tube 52 and the locknut 84 before reaching the tension rod. Thus, the insulator tubethermally isolates the tension rod from the rotor core.

[0071] The coil winding is also supported by the channel housing 44 (seeFIG. 8). The channel housing supports the coil winding againstcentrifugal forces (arrow 100 in FIG. 7) and tangential torque forces(arrow 102). The channel housing may be formed of non-magnetic metallicmaterials, such as aluminum, Inconel, and titanium alloys. The channelhousing is held in place on the tension rod by dowel 80 that extendsthrough an aperture 104 in the end of the tension rod. The legs 106 ofthe channel housing may be thick and have ribs to provide structuralsupport around the apertures 108 that receive the dowel. Centrifugalforces arise due to the rotation of the rotor. Tangential forces mayarise from acceleration and deceleration of the rotor, as well as torquetransmission. Because the sides 40 of the coil winding are encased bythe channel housings 44 and the ends 86 of the tension bars, the sidesof the coil winding are fully supported within the rotor.

[0072] A support bracket 124 is provided to assist the tension rods andchannel housing withstand the large radial forces that can result when agrid fault condition occurs. The radial support may be a rectangular boxthat fits around the sides 40 of the coil winding and extends over thesplit-clamp 58. The support bracket include a pair of side walls thatare dovetailed into a slot in the recessed surface. The side-wallsextend from the rotor core surface 48 to the shell 90 and providesstructural strength to the shell.

[0073] FIGS. 9 to 11 show schematically the assembly process for thecoil support structure and coil winding in the rotor. As shown in FIG.9, before the rotor core is assembled with the collars and othercomponents of the rotor, the tension rods 42 are inserted into each ofthe conduits 46 that extend through the rotor core. The insulator tube52 at each end of each tension rod is placed in the expanded end 88 ateach end of the conduits 46. The tube 52 is locked in place by aretainer locking-nut 84. When the tension rods are assembled in therotor core 22, the coil windings are ready to be inserted onto the core.

[0074] As shown in FIG. 10, the SC coil 36 is inserted onto the rotorcore such that the flat ends 86 of the tension rods 42 abut the insidesurface of the side sections 40 of the SC coil. Once the winding hasbeen inserted over the ends of the tension bar, the channel housings 44are inserted over the SC coil. The channel housings are secured to theends of the tension bars by inserting dowels 80 through the apertures inthe tension rod and channel housing 104, 108, respectively.

[0075] The channel housing 44 includes a slot 110 along its upper insidesurface which receives the cooling conduit 38 and holds that conduitagainst the coil 36.

[0076] The plurality of channel housings effectively hold the coil inplace without affectation by centrifugal forces. Although the channelhousings are shown as having a close proximity to one another, thehousings need only be as close as necessary to prevent degradation ofthe coil caused by high bending and tensile strains during centrifugalloading, torque transmission, and transient fault conditions.

[0077] The channel housings and tension rods may be assembled with thecoil winding before the rotor core and coils are assembled with thecollar and other components of the rotor. Accordingly, the rotor core,coil winding and coil support system can be assembled as a unit beforeassembly of the other components of the rotor and of the synchronousmachine.

[0078]FIG. 11 shows the assembly of the split clamp 58 that is formed byclamp plates 60. The clamp plates 60 sandwiched between them the endsections 64 of the coil winding. The split clamp provides structuralsupport for the ends of the coil winding 34. The plates 60 of the splitclamp include on their inside surfaces channels 116 that receive thecoil winding. Similarly, the plates include channels 118 for theinput/output lines 112 for the gases and for the input and outputcurrent connections 114 to the coil. Once the coil supports, coil,collar and rotor core are assembled, this unit is ready to be assembledinto the rotor and synchronous machine.

[0079] While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover allembodiments within the spirit of the appended claims.

What is claimed is:
 1. In a synchronous machine, a rotor comprising: arotor core having at least one conduit extending through the core; asuperconducting coil winding extending around at least a portion of therotor core, said coil winding having a pair of side sections on oppositesides of said rotor core; at least one tension rod extending between thepair of side sections of the coil winding and through said at least oneconduit of the rotor; and an insulator in the conduit thermallyseparating the tension rod from the rotor.
 2. In a rotor as in claim 1wherein said insulator is a tube having an outside surface in contactwith said conduit.
 3. In a rotor as in claim 1 wherein said insulator isa tube having an inside surface in contact with an attachment on an endof said rod.
 4. In a rotor as in claim 1 wherein the rotor core is asolid core and said conduit extends through the solid core.
 5. In arotor as in claim 1 further comprising an outside ring at one end of thetube in contact with the conduit, and an inside ring at an opposite endof the tube in contact with a lock-nut at the end of the rod.
 6. In arotor as in claim 1 wherein the insulator is formed of a composite fibermaterial.
 7. In a rotor as in claim 1 wherein the insulator is in theconduit and is adjacent an outside surface of the core.
 8. In a rotor asin claim 1 further comprising a locking-nut securing the insulator tothe conduit in the core.
 9. In a rotor as in claim 8 wherein thelocking-nut compresses the insulator into the conduit.
 10. In a rotor asin claim 9 wherein said insulator is a tube compressed by the lock-nut.11. In a rotor as in claim 1 wherein said tension rod is formed of ahigh-strength and non-metallic metal alloy.
 12. In a rotor as in claim 1wherein said tension rod is formed of an Inconel metal alloy.
 13. In arotor as in claim 1 wherein said tension rod extends through alongitudinal axis of the rotor.
 14. In a rotor as in claim 1 whereinsaid at least one tension rod is a plurality of tension rods extendingthrough a plurality of conduits in said rotor core, and said at leastone insulator is a tube insulator mounted in each end of said conduits.15. In a rotor as in claim 1 wherein said tension rod is spaced fromrotor walls of the conduits by said insulator.
 16. In a rotor furthercomprising a coil housing at an end of said tension rod, wherein saidhousing is attached to said coil winding and is attached to said tensionrod.
 17. A method for supporting a superconducting coil winding on arotor core of a synchronous machine comprising the steps of: e.extending a tension rod through a conduit in said rotor core; f.supporting the tension rod in the conduit by a first insulator tube; g.inserting a housing over a portion of the h. attaching an end of thetension rod to the housing.
 18. A method as in claim 17 furthercomprising: e. inserting a second insulator tube into an end of theconduit opposite to a conduit end in which the first insulator tube isinserted, and f. a second housing over a second portion of the coil andattaching the second housing to a second end of the tension bar.
 19. Amethod as in claim 17 wherein the first insulator tube has an outsidering at a first end of the tube and an inside ring at a second end ofthe tube, and the insulating tube is inserted into the conduit such thatthe outside ring contacts a conduit wall, and the inside ring is incontact with an attachment on the rod.
 20. A method as in claim 17further comprising compressing the insulator tube into the conduit. 21.A method as in claim 20 wherein a nut compresses the tube into theconduit.